Simplify the following expression: $k = \dfrac{7}{4z} - \dfrac{3}{10z}$
Solution: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4z$ and $10z$ $\lcm(4z, 10z) = 20z$ $ k = \dfrac{5}{5} \cdot \dfrac{7}{4z} - \dfrac{2}{2} \cdot \dfrac{3}{10z} $ $k = \dfrac{35}{20z} - \dfrac{6}{20z}$ $k = \dfrac{35 -6}{20z}$ $k = \dfrac{29}{20z}$